Any number, either national or international, independently from the involved operators.
The charge for the first message is the same of a standard SMS, all the following dispatches use the GPRS channel (which cost is derisive and depends exclusively on the number of exchanged characters, not from the duration of the connection, neither from the called Country).
The only thing that matters is that both the caller and the called must have MoIP installed on their own telephone.

MoIP sends a SMS to the phone of the recipient using a specific port number. Since all mobile phones normally don't intercept messages sent in such way, the receiver won't acknowledge anything.

Absolutely no. The application spontaneously activates itself only when another person tries to contact us through MoIP.
The only thing that matters is that both the caller and the called must have MoIP installed on their own telephone.

The typical cost for the dispatch of a SMS is – for the Italian operators – about 15 €cents per message, independently from its length (provided that you do not overcome the 160 characters limit, otherwise it will results in a dispatch of multiple messages, everyone with a charge of 15 €cents).
The GPRS charge, instead, is computed on the base of network traffic (measured in KBytes) to a maximum cost of 0,6 €cents for KB, that is less than a cent for more than 1000 characters!
A parte il primo SMS, dunque, tutti gli invii successivi vengono a costare meno di un millesimo di euro (contro i 12-15 cent ordinari).
Practically, the more you write the more greater is the saving in comparison to the traditional dispatch of SMSs (see the following chart).

NOTICE: The number of characters in the first column is to intend as the total of the dispatches towards the same phone number, not for single exchanged message (e.g., the 18 cents in charge of whom sends - second line of the preceding chart, third column - refer to a comprehensive dispatch of 500 characters during the whole communication, independently from the number of exchanged messages).

MoiP sets up a direct connection between the telephone of the caller and the one of the receiver, using the GPRS channel (more inexpensive and not subjected to time tariffs) to send messages.
The first SMS is necessary to allow the two devices to 'discover each other' reciprocally, so that to "hijack" all the following exchange of messages (either a simple answer or a more articulated chit chat) on the GPRS channel taking advantage of cheaper tariffs.

Yes, but always keep in mind that we are speaking of dispatches and receipts on the GPRS channel, that lead to particularly low fees.
Moreover, whoever receives a message then usually answers in turn, exposing himself/herself to the charge of a standard SMS. With MoiP such cost can decrease up to 20 or even 30 times.

Absolutely no since you're using a GPRS connection for the exchange of messages.
The cost is proportional to how many characters are exchanged among the sender and the receiver, not to the duration of the connection. Therefore, hypothetically, you could keep waiting for an answer for hours without spending anything, because within that time slice there is no exchange of data among the terminals (in the practice, nevertheless, it is more likely that after a certain number of seconds passed by without any answer the connection is automatically closed by the operator and therefore a timeout error is raised).

No, the communication is completely asyncronous, therefore both of the two endpoints can freely write messages to each other. If a message is received while you're writing a new one, you'll be able to read it once returned to the previous screen.

It is possible only for "signed" applications, that is signed with a digital certificate released by a competent authority.
Since MoIP is freeware, we chose not to resort the purchase and the maintenance of such certificate (which it is subjected to an annual canon) for non commercial uses of the application.

Our suggestion is to download MoiP directly on your own smartphone because this way the installation remains simple and straight forward and it is entirely automated.
Obviously nothing prevents you from downloading the application through the browser of your PC and then to install it on your phone via Bluetooth or irDA (simply download the two jad and jar files from this site and transfer them both on your smartphone). Nevertheless, since this procedure may vary according to the software used for transferring data from the PC to the phone, the installation could request more time or even require some additional steps. Furthermore not all phone models currently support Bluetooth.

Miliaris does not keep track of messages (either sent or received) in any way (otherwise we would deal with a heavy violation of the privacy), as well as of nicknames.
Even the phone numbers of the caller and the receiver are never transmitted on the GPRS channel during the conversation.
Furthermore MoiP does not depend on any external service, so no username or password of any kind are required.

Nothing.
The tool is freeware (for non commercial uses) and not even a cent of the traffic spent by the users does end in our pockets.
Being ourselves simple consumers, we have looked for a (legal) way to save something on the SMSs dispatching.
Nothing more.
Enjoy!